In our daily lives, various electronic devices such as power adapters, transformers, power supply apparatuses, electrical connectors and the like are widely used. Since the internal electronic components and the circuits of these electronic devices need to be appropriately isolated and protected, these electronic devices are usually covered by cases to avoid the contact with the external environment. The assembly structure of the case and the assembling method thereof may indirectly influence the appearances and the electric properties of the electronic apparatuses or accessories. It is important to design an appropriate case assembly structure.
Referring to FIG. 1, a schematic cross-sectional view of a conventional case assembly structure is illustrated. As shown in FIG. 1, the case assembly structure includes an upper case 1 and a lower case 2. The upper case 1 has a first connection portion 11. Corresponding to the first connection portion 11, the lower case 2 has a second connection portion 21. When the first connection portion 11 and the second connection portion 21 are engaged with each other, the upper case 1 and the lower case 2 are combined together to implement the case assembly structure.
FIG. 2 is a schematic partial enlarged view illustrating the first connection portion 11 of the upper case 1 and the second connection portion 21 of the lower case 2. From the external side 110 to the internal side 111 of the upper case 1, the first connection portion 11 of the upper case 1 includes a first protrusion 112, a first trench 113 and a second protrusion 114. From the external side 210 to the internal side 211 of the lower case 2, the second connection portion 21 of the lower case 2 includes a first concave portion 212, a third protrusion 213 and a second concave portion 214 facing to the first protrusion 112, the first trench 113 and the second protrusion 114 of the first connection portion 11, respectively. In addition, the third protrusion 213 of the second connection portion 21 has a protruding rib 215 thereon, and the width of the third protrusion 213 is slightly smaller than that of the first trench 113 of the first connection portion 11. When the third protrusion 213 of the second connection portion 21 is inserted into the first trench 113 of the first connection portion 11, the upper case 1 and the lower case 2 are combined together.
Please refer to FIGS. 3A and 3B, which are schematic cross-sectional views showing the assembling process of the case assembly structure in FIG. 2. As shown in FIG. 3A, for assembling the upper case 1 and the lower case 2, the first protrusion 112, the first trench 113 and the second protrusion 114 of the upper case 1 are firstly placed to face to the first concave portion 212, the third protrusion 213 and the second concave portion 214 of the lower case 2, respectively. Then, according to an ultrasonic welding technology, the ultrasound generated by the horn of an ultrasonic plastic welding machine produces ultra-frequent sonic vibration on the cases. Under this circumstance, the upper case 1 and the lower case 2 rub against each other violently and thus the protruding rib 215 on the third protrusion 213 of the lower case 2 can be molten and welded into the inner wall of the first trench 113 of the upper case 1 in a very short time, as can be seen in FIG. 3B. Meanwhile, the purpose of assembling the upper case 1 and the lower case 2 is achieved.
However, after the upper case 1 and the lower case 2 are assembled, the creepage distance formed between the connection portions 11 and 21 is not long enough. As a consequence, the electric leakage may occur, which indirectly influence the electric properties of the electronic device. Moreover, since the bonding strength between the upper case 1 and the lower case 2 is insufficient, the electronic device fails to withstand a stronger impact. For solving these drawbacks, the thicknesses of the connection portions 11 and 21 need to be greater than 3 mm, which increases material consumption. Moreover, for increasing the creepage distance, the length of the second protrusion 114 of the first connection portion 11 should be long enough. In a case that an external force perpendicular to the external sides of the connection portions 11 and 21, the second protrusion 114 or even the case assembly structure is readily fractured due to the structural fragility.
Therefore, there is a need of providing a case assembly structure having increased creepage distance and bonding strength so as to overcome the disadvantages of the prior art as described above.